Journal articles on the topic 'Thrust faults (Geology) Australia'
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1
Cape, C. D., R. M. O'Connor, J. M. Ravens, and D. J. Woodward. "Seismic expression of shallow structures in active tectonic settings in New Zealand." Exploration Geophysics 20, no. 2 (1989): 287. http://dx.doi.org/10.1071/eg989287.
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Late Cenozoic deformation along the Australian/Pacific plate boundary is seen in onshore New Zealand as zones characterised by extension- or transcurrent- or contraction-related structures. High-resolution multichannel seismic reflection data were acquired in several of these tectonic zones and successfully reveal the shallow structures within them. Thirty kilometres of dynamite reflection data in the Rangitaiki Plains, eastern Bay of Plenty, define a series of NE-trending normal faults within this extensional back-arc volcanic region. The data cross surface ruptures activated during the 1987 Edgecumbe earthquake. In the southern North Island, a 20 km Mini-Sosie? seismic profile details the Quaternary sedimentation history and reveals the structure of the active strike-slip and thrust fault systems that form the western and eastern edges of the Wairarapa basin, respectively. This basin is considered to sit astride the boundary between a zone of distributed strike-slip faults and an active accretionary prism. In the Nelson area, northwestern South Island, previously unrecognised low-angle thrust faults of Neogene or Quaternary age are seen from Mini-Sosie data to occur at very shallow depths. Crustal shortening here was previously thought to arise from movement on high-angle reverse faults, and the identification of these low-angle faults has prompted a reassessment of that model. A grid of 18 km of Mini-Sosie seismic data from the central eastern South Island delineates Neogene or Quaternary thrust faults in Cenozoic sediments. The thrusts are interpreted as reactivated Early Eocene normal faults, and the thrust fault geometry is dominated by these older structures.
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Scherrenberg, Arne F., and Gideon Rosenbaum. "Photograph of the Month: Thrust duplex, low-angle normal faults and domino-style faults in laminated shale, Mt Isa, Australia." Journal of Structural Geology 31, no. 5 (May 2009): 475. http://dx.doi.org/10.1016/j.jsg.2008.10.015.
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Robinson, Russell, Rafael Benites, and Russ Van Dissen. "Evidence for temporal clustering of large earthquakes in the wellington region from computer models of seismicity." Bulletin of the New Zealand Society for Earthquake Engineering 31, no. 1 (March 31, 1998): 24–32. http://dx.doi.org/10.5459/bnzsee.31.1.24-32.
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Temporal clustering of large earthquakes in the Wellington region, New Zealand, has been investigated with a computer model that generates long synthetic seismicity catalogues. The model includes the elastic interactions between faults. Faults included in the model, besides the subduction thrust between the Australian and Pacific plates, are segments of the four major strike-slip faults that overlie the plate interface (Wairarapa, Wellington, Ohariu, and Wairau faults). Parameters of the model are adjusted to reproduce the geologically ohserved slip rates of the strike-slip faults. The seismic slip rate of the subduction thrust, which is unknown, is taken as 25% of the maximum predicted by the plate tectonic convergence rate, and its position fixed according to recent geodetic results. For comparison, the model was rerun with the elastic interactions suppressed, corresponding to the usual approach in the calculation of seismic hazard where each fault is considered in isolation. Considering earthquakes of magnitude 7.2 or more ("characteristic" events in the sense that they rupture most of a fault plane). the number of short (0-3 years) inter-event times is much higher with interactions than for the corresponding case without interactions (46% vs. 2% or all inter-event times). This reduces to 9% vs. 2% if the subduction thrust is removed from the models. Paleoseismic studies of the past seismic behaviour of the subduction thrust are clearly needed if the degree of clustering is to be tightly constrained. Although some other aspects of our model can he improved in future, we think that the probability of significant short-term clustering of large events, normally neglected in hazard studies, is very high. This has important implications for the engineering, insurance and emergency response communities.
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Dinc, Gulce, Jean-Paul Callot, and Jean-Claude Ringenbach. "Shale mobility: From salt-like shale flow to fluid mobilization in gravity-driven deformation, the late Albian–Turonian White Pointer Delta (Ceduna Subbasin, Great Bight, Australia)." Geology 51, no. 2 (December 20, 2022): 174–78. http://dx.doi.org/10.1130/g050611.1.
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Abstract Large offshore depocenters above a weak detachment level (either salt or shale) can undergo gravity spreading and/or gliding. The gravitational systems (e.g., gliding deltas) are classically composed of an updip domain affected by extensional listric normal faults and a downdip domain affected by toe thrusts. While the role of salt in such systems is a classic tectonic process, the role and mechanical behavior of mobile shale levels in shale-prone gravity-driven systems are increasingly questioned. A three-dimensional seismic data set in the Ceduna Subbasin (Australia) displays the late Albian–Turonian White Pointer Delta (WPD) as having an unusual diversity of shale-cored structures. The early flow of shale resulted in depocenters showing wedges, internal unconformities, and shale diapirs and ridges, while fluidization of shales underneath a significant burial resulted in mud volcanism, secondary radial fault sets, and collapse features beneath the Campanian–Maastrichtian Hammerhead Delta, which lies above the WPD. Massive shale mobilization, together with downdip shortening and distal margin uplift, localized a major thrust in the core of the basin, ending the downward-propagating failure of the WPD. Mobilization of thick shale intervals, either as salt-like flow or mud volcanism, appears to have been a key process in the deformation, which should be considered at large scale for worldwide gravity-driven deformation systems.
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Clarke, C. J., R. J. George, R. W. Bell, and R. J. Hobbs. "Major faults and the development of dryland salinity in the western wheatbelt of Western Australia." Hydrology and Earth System Sciences 2, no. 1 (March 31, 1998): 77–91. http://dx.doi.org/10.5194/hess-2-77-1998.
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Abstract. Dryland salinity poses a major threat to agricultural production in the wheatbelt of Western Australia and much time and effort is expended on understanding the mechanisms which cause it and on developing techniques to halt or reverse its development. Whilst the location of much dryland salinity can be explained by its topographic position, a significant proportion of it cannot. This study investigated the hypothesis that major faults in the Yilgarn Craton represented in aeromagnetic data by intense curvilinear lows explained the location of areas of dryland salinity not explained by topography. Moreover, the causal mechanisms that might underpin a spatial relationship between major faults and dryland salinity were sought. In one fourth order catchment, nearly 85% of the salinity that was not explained topographically was within 2km of the centre line of a major fault, the remaining 15% being in the other 12km of the catchment. Three groups of similar third order catchments in the western wheatbelt of Western Australia were also investigated; in each case the catchment that was underlain by a major fault had dryland salinity an order of magnitude more than the unfaulted catchment(s). This evidence demonstrates a strong spatial association between major faults and the development of dryland salinity. Other evidence suggests that the underlying mechanism is hydraulic conductivity 5.2 to 2.9 times higher inside the fault zone compared to outside it and shows that geomorphology, salt store, regolith thickness, and degree of clearing are not the underlying mechanisms. In one of the groups of catchments, it has been calculated that an amount of recharge, significant in relation to recharge from rainfall, was entering from an adjacent catchment along a major fault. The paper concludes that geological features such as major faults affect the development of dryland salinity in the wheatbelt of Western Australia because of permeability differences in the regolith and therefore computer models of salinity risk need to take these differences into account. Techniques need to be developed to map, quickly and relatively cheaply, the geology-related permeability differences over wide areas of the landscape.
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McDivitt, Jordan A., Steffen G. Hagemann, Nicolas Thébaud, Laure A. J. Martin, and Kai Rankenburg. "Deformation, Magmatism, and Sulfide Mineralization in the Archean Golden Mile Fault Zone, Kalgoorlie Gold Camp, Western Australia." Economic Geology 116, no. 6 (September 1, 2021): 1285–308. http://dx.doi.org/10.5382/econgeo.4836.
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Abstract The Golden Mile fault zone is a key controlling structure to the estimated 75 Moz gold endowment of the Kalgoorlie gold camp in the Yilgarn craton of Western Australia. The earliest structures in the fault are F1 folds that developed during D1 recumbent-fold and thrust deformation (<2685 ± 4 Ma). These F1 folds are overprinted by a pervasive NW- to NNW-striking S2 cleavage related to sinistral shearing beginning with 2680 ± 3 Ma D2a sinistral strike-slip and culminating with ca. 2660 Ma D2c sinistral-reverse movement. The majority of deformation in the fault zone correlates to ca. 2675 Ma D2b deformation, which is characterized by sinistral-normal kinematic indicators. Late, ca. 2650–2640 Ma D3 dextral-reverse kinematic indicators overprint the earlier D2 structures. Pyrrhotite-chalcopyrite-pyrite-sphalerite-galena assemblages were emplaced throughout the D2 event within NE-trending D2a tensile fractures, NW- to NNW-striking D2b normal faults and associated breccias, and NW- to NNW-striking D2c low-angle veins, with the latter D2b and D2c structures correlating to the Fimiston and Oroya mineralization types, respectively. All D2a-, D2b-, and D2c-related sulfides in the Golden Mile fault zone show similarly restricted δ34S (~1.0–4.5‰) and elevated Δ33S (~2.0–3.0‰) values that reflect strong local sulfur contribution from shales of the Lower Black Flag Group and host-rock buffering of hydrothermal fluids related to the Fimiston and Oroya mineralization events. This host-rock buffering decreased fluid fO2, favoring the development of pyrrhotite-pyrite stable sulfide assemblages and causing respective decreases and increases in fluid Au-Te and Pb-Bi-Sb concentrations. At the camp scale, the Golden Mile fault zone exerted a primary control on the distribution of porphyry dikes and gold deposits; however, magma and hydrothermal fluid circulation was favored in adjacent, higher-order structural sites due to the fault zone’s incompetent rheology and tendency for ductile deformation and diffuse fluid flow. Other Archean examples such as Au deposits of the Larder Lake-Cadillac deformation zone in the Superior craton illustrate that this type of diffuse fluid flow in large-scale crustal fault zones can result in disseminated economic mineralization. However, this study highlights that host-rock effects on fluid chemistry in large-scale crustal fault zones exercises a strong control on a fluid’s propensity to form ore. The results of this study emphasize that both the rheology and chemistry of rocks within and adjacent to large-scale deformation zones act as important controls on the formation of gold ore in Archean terranes.
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Polawan, S. M., and N. A. Raharjanti. "Preliminary Study of Landslide Hazard in Kutai Kartanegara Regency, East Kalimantan using Digital Elevation Model." IOP Conference Series: Earth and Environmental Science 1071, no. 1 (August 1, 2022): 012007. http://dx.doi.org/10.1088/1755-1315/1071/1/012007.
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Abstract The Kalimantan Island is part of the Sundaland crust, namely the Eurasian Continental Plate. The plate is moving to the southeast colliding with the Indo-Australian plate which is moving north. Whereas for Kutai Kartanegara Regency in the Kalimantan Island position is far from the collision zone, so it is relatively stable tectonically. This is important to research that is, due to tectonic processes that occurred earlier, resulting in the formation of geological structures, especially faults. The purpose of the study was to determine the morphotectonic and landslide hazards in the Kutai Kartanegara Regency, where this research was carried out quantitatively with data collection techniques, then analyse landslide hazards based on data; DEM (Digital Elevation Model) including the slope, slope direction, and slope length for vulnerability analysis, geological data from Regional Geological Maps, which include rock formations, distances from faults data and administrative boundary spatial data in the form of vector GIS for the preparation of landslide hazard maps. The result showing Kutai Kartanegara predominantly categorized as moderate to high hazard zone. The low hazard zone covering 9.88% area, moderate hazard zone covering 35.81% area, and 54.31% area is high hazard zone of landslide. The analysis showing that the hazard of the research area consist predominantly sedimentary rocks and controlled by structural geology identified as thrust fault, strike slip fault, and fold which include in Anticlinorium Samarinda. Those lithology and geological structure features along with the slope are identified as controlling factor to the landslide hazard in the research area.
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Bendall, M. R., J. K. Volkman, D. E. Leaman, and C. F. Burrett. "RECENT DEVELOPMENTS IN EXPLORATION FOR OIL IN TASMANIA." APPEA Journal 31, no. 1 (1991): 74. http://dx.doi.org/10.1071/aj90007.
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Recent work on oil seeps, organic geochemistry, geophysics, structural geology and palaeontology suggests that there is considerable potential for onshore petroleum in Tasmania.Archival research has shown that hydrocarbon seeps were commonly reported in the first half of this century and that wildcats produced gas (at Port Sorell in the north) and oil (at Johnson's Well on Bruny Island, in the south). Almost all of the 270 historical hydrocarbon occurrences lie on lineaments revealed independently by gravity and magnetic surveys. The thermal maturity of conodonts from Ordovician and Siluro-Devonian carbonates suggests that much of the pre-Upper Carboniferous beneath the Tabberabberan unconformity is within the oil and gas windows.Organic geochemistry reveals a very close similarity between hydrocarbons from Ordovician limestones, those from the drill site at Bruny Island and with tar samples from the Tasmanian coast, but little similarity with the Permian Tasmanite Oil Shale, or with the Gippsland crudes and botryococcane-rich South Australian bitumens. The predominance of C27 steranes in Tasmanian bitumens suggests a widespread algal source and the abundant diasteranes imply a clay or silt-rich source that extends across much of Tasmania.Recent geophysical and structural work suggests that a thin skinned interpretation of Tasmania's structure is reasonable. Most sightings of hydrocarbons are associated with either faults or fractures which have post-Jurassic displacements or with intersections of major high angle faults with thrusts. The delineation of reservoirs within the thrust sheets is a priority.
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Wex, Sebastian, Neil S. Mancktelow, Friedrich Hawemann, Alfredo Camacho, and Giorgio Pennacchioni. "Inverted distribution of ductile deformation in the relatively “dry” middle crust across the Woodroffe Thrust, central Australia." Solid Earth 9, no. 4 (July 11, 2018): 859–78. http://dx.doi.org/10.5194/se-9-859-2018.
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Abstract. Thrust fault systems typically distribute shear strain preferentially into the hanging wall rather than the footwall. The Woodroffe Thrust in the Musgrave Block of central Australia is a regional-scale example that does not fit this model. It developed due to intracontinental shortening during the Petermann Orogeny (ca. 560–520 Ma) and is interpreted to be at least 600 km long in its E–W strike direction, with an approximate top-to-north minimum displacement of 60–100 km. The associated mylonite zone is most broadly developed in the footwall. The immediate hanging wall was only marginally involved in the mylonitization process, as can be demonstrated from the contrasting thorium signatures of mylonites derived from the upper amphibolite facies footwall and the granulite facies hanging wall protoliths. Thermal weakening cannot account for such an inverse deformation gradient, as syn-deformational P–T estimates for the Petermann Orogeny in the hanging wall and footwall from the same locality are very similar. The distribution of pseudotachylytes, which acted as preferred nucleation sites for shear deformation, also cannot provide an explanation, since these fault rocks are especially prevalent in the immediate hanging wall. The most likely reason for the inverted deformation gradient across the Woodroffe Thrust is water-assisted weakening due to the increased, but still limited, presence of aqueous fluids in the footwall. We also establish a qualitative increase in the abundance of fluids in the footwall along an approx. 60 km long section in the direction of thrusting, together with a slight decrease in the temperature of mylonitization (ca. 100 °C). These changes in ambient conditions are accompanied by a 6-fold decrease in thickness (from ca. 600 to 100 m) of the Woodroffe Thrust mylonitic zone.
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Pettinga, Jarg R., Mark D. Yetton, Russ J. Van Dissen, and Gaye Downes. "Earthquake source identification and characterisation for the Canterbury region, South Island, New Zealand." Bulletin of the New Zealand Society for Earthquake Engineering 34, no. 4 (December 31, 2001): 282–317. http://dx.doi.org/10.5459/bnzsee.34.4.282-317.
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The Canterbury region of the South Island of New Zealand straddles a wide zone of active earth deformation associated with the oblique continent-continent collision between the Australian and Pacific tectonic plates east of the Alpine fault. The associated ongoing crustal strain is documented by the shallow earthquake activity (at depths of <40 km) and surface deformation expressed by active faulting, folding and ongoing geodetic strain. The level of earth deformation activity (and consequent earthquake hazard) decreases from the northwest to the southeast across the region. Deeper-level subduction related earthquake events are confined to the northernmost parts of the region, beneath Marlborough.
To describe the geological setting and seismological activity in the region we have sub-divided the Canterbury region into eight domains that are defined on the basis of structural styles of deformation. These eight domains provide an appropriate geological and seismological context on which seismic hazard assessment can be based. A further, ninth source domain is defined to include the Alpine fault, but lies outside the region.
About 90 major active earthquake source faults within and surrounding the Canterbury region are characterised in terms of their type (sense of slip), geometry (fault dimensions and attitude) and activity (slip rates, single event displacements, recurrence intervals, and timing of last rupture). In the more active, northern part of the region strike-slip and oblique strike-slip faults predominate, and recurrence intervals range from 81 to >5,000 years. In the central and southern parts of the region oblique-reverse and reverse/thrust faults predominate, and recurrence intervals typically range from -2,500 to >20,000 years.
In this study we also review information on significant historical earthquakes that have impacted on the region (e,g. Christchurch earthquakes 1869 and 1870; North Canterbury 1888; Cheviot 1902; Motunau 1922; Buller 1929; Arthurs Pass 1929 and 1994; and others), and the record of instrumental seismicity. In addition, data from available paleoseismic studies within the region are included; and we also evaluate large potential earthquake sources outside the Canterbury region that are likely to produce significant shaking within the region. The most important of these is the Alpine fault, which we include as a separate source domain in this study.
The integrated geological and seismological data base presented in this paper provide the foundation for the probabilistic seismic hazard assessment for the Canterbury region, and this is presented in a following companion paper in this Bulletin (Stirling et al. this volume).
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Rynn, J. M. W., E. Brennan, P. R. Hughes, I. S. Pedersen, and H. J. Stuart. "The 1989 Newcastle, Australia, earthquake." Bulletin of the New Zealand Society for Earthquake Engineering 25, no. 2 (June 30, 1992): 77–144. http://dx.doi.org/10.5459/bnzsee.25.2.77-144.
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The vulnerability of urban environments in continental regions to earthquake forces was explicitly demonstrated in Australia's devastating Newcastle earthquake on December 28, 1989. This moderately-sized earthquake of Richter magnitude ML 5.6 (Moment magnitude M 5.3) claimed 13 lives, damaged more than 70,000 properties and left an estimated total loss of about $AU (1991) 4 billion. The need for an earthquake mitigation programme in Australia was thus clearly established. It is for this reason that a multidisciplinary approach involving seismology, geology, engineering, insurance, local government and emergency services is being followed to study this event and its consequences.
The earthquake source is defined as being on a thrust fault trending NW-SE dipping 75° to the NE, with a depth of focus at 11.5 km, source radius of 1.86 km, stress drop of at least 24 bars and a displacement along the rupture surface of at least 310 mm. The epicentre is located at 32.95°S, 151.61°E close to Boolaroo, about 15 km SW of the City of Newcastle, and with an epicentral error of about + 15 km. More than 100,000 observations from damage and felt reports are being analysed and integrated with the wide experiences gained in the rescue, recovery and renewal phases that have extended over the two years since the event.
The specific issue of the geotechnical aspects is of great importance. It is being considered from the view of urban geology (surface alluvial sediments), rather than from theoretical considerations, to explain the major extent of building damage on the alluvial areas, amplification and liquefaction. Apart from the immediate "causes" of damage, serious consideration is being given to the long-term effects which have resulted in the latent and recurrent defects to buildings. The engineering findings from the Newcastle earthquake are discussed in detail. While it is uneconomical and not necessary to design a structure to withstand the greatest likely earthquake without damage in Australia, the cost of providing strength to resist very high intensity loads must be weighed against the importance of the structure and probability of the earthquakes, particularly in areas such as this with relatively little known seismic histories. Lessons for local government authorities who had not previously considered seismic activity are addressed. Based on the response and recovery of the City of Newcastle, the lessons include the development of a recovery management plan, revision of building regulations and the requirements for hazard mitigation. Unfortunately, several misconceptions about some aspects of the consequences of this earthquake have arisen. These concern the limitations of some analyses, use of selected data sets rather than all the available data and apparent lack of understanding of complex, rather than singular, causal relationships. Implications for the engineering, insurance and possibly the legal professions need to be considered.
The potential to reduce losses in future earthquakes in Australia through an earthquake mitigation programme is now an achievable goal. The scenarios of such an event occurring at a different time or in a different city can be addressed, based on the Newcastle and other international experiences. Sufficient information is available to prepare the revised Australian earthquake loading code as a reliable and practical document for use by engineers. The consequences of the 1989 Newcastle earthquake have also captured the interest of researchers from many other continental areas of the Earth who must consider preparations for similar situations. All aspects of the study ultimately lead to the preparedness of urban communities to deal with such consequences with the assistance of emergency services agencies to minimize the social and economic traumas that will inevitably occur.
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Martinez, Alexandra, Jacques Malavieille, Serge Lallemand, and Jean-Yves Collot. "Strain partitioning in an accretionary wedge, in oblique convergence : analogue modelling." Bulletin de la Société Géologique de France 173, no. 1 (January 1, 2002): 17–24. http://dx.doi.org/10.2113/173.1.17.
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Abstract In subduction zones undergoing oblique convergence, strain partitioning is often expressed by an important deformation inducing strike-slip faulting. In accretionary wedges, parameters such as obliquity of the convergence and friction at the bottom of the wedge play an important role in the strain partitioning. The impact of these parameters is studied using sandbox experiments. Two backstop geometries have been designed to account for different geological settings. These experiments show that the wedge taper remains constant and close to αcoulomb for variable obliquities. Measurements of critical tapers on the models suggest that the Coulomb wedge theory cannot be simply applied to determine parameters on wedges developed under oblique convergence. Parameters deduced from this theory are valid only when measured in the direction parallel to the convergence. In addition, the partition degree increases with the obliquity of the convergence, and strain partitioning occurs independently of the basal friction. We remark that the model morphology changes when an obliquity value, mainly, is exceeded. A transcurrent structure develops. The models show that oblique structures located above the velocity discontinuity are associated with strike-slip faults. Similar structures have been observed within the Hikurangi accretionary wedge (New Zealand). Introduction. – In subduction zones, for high values of the convergence obliquity γ, transcurrent faults are observed, parallel to the trench, on the continental plate. Such structures are present in Sumatra and the Philippines along the volcanic arc [Bellier and Sébrier, 1995 ; Malod et al., 1993 ; Barrier et al. 1991] or at the rear of the accretionary wedge for the South Ryukyu (Taiwan). These strike-slip faults are a consequence of strain partitioning. Partition is controlled by obliquity of convergence, basal friction and probably geometry of backstop. Using analog models, the influence of each parameter on strain partitioning, on the occurrence of transcurrent faults and its morphology are analyzed. The strain partitioning can be quantified by its degree (1) \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[K_{\mathit{v}}\ =\ (1\ {-}\ \frac{{\phi}}{{\gamma}})\ {\cdot}\ 100\] \end{document} It requires the knowledge of the slip vector, which is situated between the azimuth of the convergence and the perpendicular to the trench. Experimental procedure. – The aim of our experiments is to better understand the effects of several parameters which determine the strain partitioning in accretionary wedges undergoing oblique convergence. For this purpose, a large-size table (140 cm × 250 cm) covered with a plastic film moving towards the backstop is used (fig. 1). The basal friction of the wedge can change according to the different textures of the plastic films used. Various angles of convergence (0o, 20o, 40o and 60o) are studied (fig. 1). Two types of backstop geometries are designed. In the first case, the plastic sheet moves under a thin PVC plate resting at the base of the material, in order to localize the strain above the velocity discontinuity, at the tip of the plate. In the second case, the backstop presents a 4 cm high, low-friction vertical wall. The whole device is covered by 2 cm of dry sand. The sand satisfies a Coulomb failure envelope, with an internal friction angle of about 30o and a very low cohesion. Colored markers perpendicular and parallel to the convergence direction, and perpendicular to the backstop, are spread on the surface of the sand. They allow recording of kinematics during the experiments. During these experiments, the plastic film converges towards the backstop with a constant velocity. Pictures of the deforming model are taken perpendicularly to the surface, every 5 cm of shortening. Intersections of the colored lines are followed and recorded at every stage of shortening, in order to describe the deformation and determine the velocity field. Vs corresponds to the displacement-vector of these points. The knowledge of the kinematics allows to deduce (using geometric construction) the slip-vector Vg and its obliquity ψ relative to the normal to the trench. The partition degree Kv is a function of the obliquity of convergence vector and of the obliquity of slip vector (fig. 2). The critical taper is measured at the end of each experiment, perpendicularly to the backstop and parallely to the direction of convergence. Results and discussion. – The morphology of the wedge suggests different structural domains : (a) a stable domain, (b) a zone of wrenching, (c) a wedge of imbricated thrusts. Above a value of the obliquity of convergence, the three domains become more distinct. Oblique structures develop in relation with the strike-slip fault. Their orientation compared with the orientation of the strike-slip fault is controlled by the geometry of the backstop (fig. 3). In the first type, these structures seem to be perpendicular to the convergence, in contrast with the second type where they tend to be parallel. Physical models of accretionary wedges show that the critical taper increases with increasing basal friction [e.g., Malavieille et al., 1992]. Furthermore, the sand used in the experiments obeys Coulomb failure criterion. Davis et al. [1983] apply this criterion to convergent thrust-wedges. They determine a relationship between critical taper wedge (αcoulomb), dip (β) of the subducting plate and basal friction (μb) : (2) \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\alpha}_{\mathit{coulomb}}\ +\ {\gamma}\ =\ \frac{({\mu}\mathit{b}\ +\ {\beta}}{(1\ +\ \mathit{K})}\] \end{document} In our experiments, for both geometries of backstop, the slope measured perpendicularly to the trench increases with the obliquity of the convergence, whereas the slope measured parallel to the direction of the convergence remains constant. Its value is close to the slope deduced from relation 1. The slope measured perpendicularly to the trench increases with increasing basal friction (fig. 4). The partition degree Kv depends on the relation between the convergence vector Vc and the slip vector Vg. Each of them is defined by their obliquities which are respectively γ and ψ. The partition degree Kv can be deduced from the obliquity of the convergence vector relative to the slip vector, Liu et al. [1995]. See equation (1). For both backstop geometries (fig. 5), Kv increases with the obliquity of the convergence γ. Moreover, the strain partitioning develops for γ superior or equal to 20o. In the second type of experiments, the partition degree is homogeneous in the whole structure. It moves like a single block along a strike-slip fault located above the velocity discontinuity (fig. 6). Studies on the critical taper allow Davis et al. [1983], to determine a relationship applied to a frontal convergence. In our experiments, the measurements of the critical taper of the accretionary wedge is equal to αcoulomb and remains constant in the direction of the convergence. The critical taper equation (2) seems to apply in the direction of convergence. So the measures taken in the direction of the convergence permit to obtain some correct parameters. Using sand-silicone analogue models, Pinet and Cobbold [1992] show that a minimum angle of oblique convergence (30o) is required before strain partitioning occurs. Our models involving dry sand clearly reveal that strain partitioning : increases with the obliquity of convergence, may develop with low obliquities and may also develop if basal friction is very low. From physical models, Chemenda et al. [2000] proposed that the strain partitioning at lithospheric scale may occur for a high interplate friction only. Thus, the rheology of the material probably has a strong influence on the critical value of the convergence obliquity beyond which strain partitioning may appear. Comparison with natural examples. – To the south of the Ryukyu Trench, northeast Taiwan, bathymetric data highlight a dextral strike-slip fault at the rear of the accretionary wedge [Lallemand et al., 1999]. Seismic profiles analysis crossing the same area gives constraints on the shape of the Ryukyu arc basement. It ends with a several kilometers high subvertical basement wall [Font et al., 2001]. This vertical backstop favors strain partitioning and locates strike slip faulting. Our models also clearly outline the impact of backstop geometry on strain partitioning and on strain location. In New-Zealand, along the Hikurangi margin, the Pacific plate meets the Australian plate at a very oblique convergence (60o). Between the Cook canyon (175o00E and 176o45E), three crustal faults, having the same direction, are observed. The Palliser-Kaiwhata fault which outlines the edge of the continental margin is interpreted as a subvertical strike-slip fault. Close to the trench, two other faults are interpreted as reverse faults which may correspond to a strike slip oblique component. Sonar data reveals a lineament associated only with the Palliser-Kaiwhata fault trend [Barnes et al., 1998]. In our experiments, oblique structures associated to strike-slip faulting developed (backstop geometry 2, fig. 3d). These structures seem to be linked with strike-slip displacement of faults. Knowing the boundary conditions of the models and about the structural surface of the Hikurangi wedge, a similar configuration to our models could exist, with the possible presence of a velocity discontinuity above the Palliser-Kaiwhata fault. The present study points out several results : the critical taper of the wedge remains stable in the direction of the convergence when the obliquity increases. It is equal to the theoretical value determined by the Coulomb wedge theory; the partition degree increases with increasing obliquity of the convergence, whatever the basal friction may be; different structural domains characterized by their morphology have been observed : a stable domain, a convergence zone of wrenching, and a wedge of imbricated thrusts; oblique structures are associated to the strike slip fault zone.
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PALASRI, CHITTI, and ANAT RUANGRASSAMEE. "PROBABILISTIC SEISMIC HAZARD MAPS OF THAILAND." Journal of Earthquake and Tsunami 04, no. 04 (December 2010): 369–86. http://dx.doi.org/10.1142/s179343111000087x.
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In this study, the probabilistic seismic hazard map of Thailand and neighboring areas is developed. Thailand is located close to the Andaman thrust in the west and the Sunda arc in the south which are the boundaries between the Eurasian plate and Indo-Australian plate. Several active faults in this region have caused earthquakes which affects Thailand. Earthquakes recorded from 1912 to 2006 by the Thai Meteorological Department and the US Geological Survey are used in the analysis. Two attenuation models for active tectonic regions which give good correlations with actual measured accelerations are used in predicting peak horizontal accelerations in Thailand. Maps of peak horizontal accelerations at rock sites with 2% and 10% probabilities of exceedance in 50 years are developed. For the peak horizontal acceleration with 10% probability of exceedance in 50 years, the maximum accelerations are about 0.25 g in the northern part of Thailand and 0.02 g in Bangkok. For the peak horizontal acceleration with 2% probability of exceedance in 50 years, the maximum accelerations are about 0.4 g in the northern part of Thailand and 0.04 g in Bangkok.
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Novikov, I. S., and D. A. Borisenko. "Geomorphology and Neotectonics of Southwestern Crimea." Russian Geology and Geophysics 62, no. 4 (April 1, 2021): 401–14. http://dx.doi.org/10.2113/rgg20194094.
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Abstract —The area of southwestern Crimea includes the ending of the Crimean Mountains that arose during the neotectonic activation at the place of the Cretaceous–Paleogene denudation plain and the adjacent shallow-water carbonate sedimentation basin. The Crimean Mountains are one of the links of the Alpine–Himalayan orogenic belt formed during the collision of the Eurasian, African, and Indo–Australian plates. Their area includes late Cenozoic marine terraces of the complete Mediterranean series and a staircase of Neogene, Paleogene and Cretaceous planation surfaces over them. The planation surfaces of different ages resulted from the successive lowering of the World Ocean level. Their subsequent deformations make it possible to outline the area of the neotectonic uplifting and determine its parameters. The main mechanism of the neotectonic activation was the thrust of the East Black Sea microplate under the Scythian one and the formation of a ramp fold structure. The amplitude of the neotectonic uplifting of southwestern Crimea for the past 2 Myr varies from 0 to 800 m, i.e., is up to 0.04 mm/year. The recent neotectonic structure of the area is formed by the northern flank of the ramp fold; it is a monocline of NW dip consisting of “keys” of NW strike separated by the latest faults with vertical displacements of 10 to 120 m. The uplifting of the area and the lowering of the World Ocean level led to a widespread of denudation surfaces. Their good preservation makes it possible to refine the sequence of neotectonic events, whose first pulses reached the study area in the Oligocene, and the main activation phase began in the Pliocene.
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Wigginton, Sarah S., Elizabeth S. Petrie, and James P. Evans. "The mechanics of initiation and development of thrust faults and thrust ramps." Mountain Geologist 59, no. 2 (April 28, 2022): 47–75. http://dx.doi.org/10.31582/rmag.mg.59.2.47.
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This study integrates the results of numerical modeling analyses based on outcrop studies and structural kinematic restorations to evaluate the mechanics of thrust fault initiation and development in mechanically layered sedimentary rocks. A field-based reconstruction of a mesoscopic thrust fault at Ketobe Knob in central Utah provides evidence of thrust ramp nucleation in competent units, and fault propagation upward and downward into weaker units at both fault tips. We investigate the effects of mechanical stratigraphy on stress heterogeneity, rupture direction, fold formation, and fault geometry motivated by the geometry of the Ketobe Knob thrust fault in central Utah; the finite element modeling examines how mechanical stratigraphy, load conditions, and fault configurations influence temporal and spatial variation in stress and strain. Our modeling focuses on the predicted deformation and stress distributions in four model domains: (1) an intact, mechanically stratified rock sequence, (2) a mechanically stratified section with a range of interlayer frictional strengths, and two faulted models, (3) one with a stress loading condition, and (4) one with a displacement loading condition. The models show that early stress increase in competent rock layers are accompanied by low stresses in the weaker rocks. The frictional models reveal that the heterogeneous stress variations increase contact frictional strength. Faulted models with a 20° dipping fault in the most competent unit result in stress increases above and below fault tips, with extremely high stresses predicted in a ‘back thrust’ location at the lower fault tip. These findings support the hypothesis that thrust faults and associated folds at the Ketobe Knob developed in accordance with a ramp-first kinematic model and development of structures was significantly influenced by the nature of the mechanical stratigraphy.
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Schavran, Gabrielle. "Structural Features in the Huerfano Park Area, East Flank, Sangre de Cristo Range, Colorado." Mountain Geologist 22, no. 1 (January 1, 1985): 33–39. http://dx.doi.org/10.31582/rmag.mg.22.1.33.
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Laramide deformation along the east flank of the Sangre de Cristo Range, Colorado, has produced an imbricate thrust system with associated major folds in the Middle Pennsylvanian Minturn Formation, west of the town of Gardner. Thrusts dip 5 to 15 degrees to the west and are offset along strike by small tear faults. Major folds are inclined to overturned near the leading edges of the thrusts and become open and diminish in amplitude to the west, farther from the leading edges. Fold axes trend between N 10 Wand N 60 Wand plunge gently to the northwest or southeast. Tectonic transport was from west-southwest to east-northeast as interpreted from ma1or thrust and fold trends. Detailed analyses of minor structures such as bedding-plane thrusts, minor folds, and angle faults substantiate the style of deformation and the interpreted direction of transport Pennsylvanian sedimentary rocks were detached and thrusted, probably above a major decollement surface. Folds, bedding thrust reverse faults, and tear faults developed during thrusting and imbrication. Regionally, Precambrian rocks to the west in the Sangre de Cristo Range are interpreted to be allochthonous suggesting that the fold and thrust belt represents a zone of Laramide crustal shortening.
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Deng, Chao, Rixiang Zhu, Jianhui Han, Yu Shu, Yuxiang Wu, Kefeng Hou, and Wei Long. "Impact of basement thrust faults on low-angle normal faults and rift basin evolution: a case study in the Enping sag, Pearl River Basin." Solid Earth 12, no. 10 (October 14, 2021): 2327–50. http://dx.doi.org/10.5194/se-12-2327-2021.
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Abstract. Reactivation of pre-existing structures and their influence on subsequent rift evolution have been extensively analysed in previous research on rifts that experienced multiple phases of rifting, where pre-existing structures were deemed to affect nucleation, density, strike orientation, and displacement of newly formed normal faults during later rifting stages. However, previous studies paid less attention to the extensional structures superimposing onto an earlier compressional background, leading to a lack of understanding of, e.g. the reactivation and growth pattern of pre-existing thrust faults as low-angle normal faults and the impact of pre-existing thrust faults on newly formed high-angle faults and subsequent rift structures. This study investigating the spatial relationship between intra-basement thrust and rift-related faults in the Enping sag, in the northern South China Sea, indicates that the rift system is built on the previously deformed basement with pervasive thrusting structures and that the low-angle major fault of the study area results from reactivation of intra-basement thrust faults. It also implies that the reactivation mode of basement thrust faults is dependent on the overall strain distribution across rifts, the scale of basement thrust faults, and the strain shadow zone. In addition, reactivated basement thrust faults influence the nucleation, dip, and displacement of nearby new faults, causing them to nucleate at or merge into downwards it, which is representative of the coupled and decoupled growth models of reactivated thrust faults and nearby new faults. This work not only provides insights into the growth pattern of rift-related faults interacting with reactivated low-angle faults but also has broader implications for how basement thrust faults influence rift structures, normal fault evolution, and syn-rift stratigraphy.
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BURBERRY, C. M., and J. M. PALU. "The influence of the Great Falls Tectonic Zone on the thrust sheet geometry of the southern Sawtooth Range, Montana, USA." Geological Magazine 153, no. 5-6 (June 3, 2016): 845–65. http://dx.doi.org/10.1017/s0016756816000431.
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AbstractThe reactivation potential of pre-existing deep-seated structures influences deformation structures produced in subsequent compression. This contribution investigates thrust geometries produced in surface thrust sheets of the Sawtooth Range, Montana, USA, deforming over a previously faulted sedimentary section. Surface thrust fault patterns were picked using existing maps and remote sensing. Thrust location and regional transport direction was also verified in the field. These observations were used to design a series of analogue models, involving deformation of a brittle cover sequence over a lower section with varying numbers of vertical faults. A final model tested the effect of decoupling the upper cover and lower section with a ductile detachment, in a scenario closer to that of the Sawtooth Range. Results demonstrate that complexity in surface thrust sheets can be related to heterogeneity within the lower sedimentary section, even when there is a detachment between this section and the rest of the cover. This complexity is best observed in the map view, as the models do not show the deep-seated faults propagating into the cover. These results were then used to predict specific locations of discrete basement fault strands in the study area, associated with what is generally mapped as the Scapegoat-Bannatyne Trend. The deep-seated faults are more likely to be reactivated as strike-slip features in nature, given the small obliquity between the ENE-directed compression direction and the NE-oriented basement faults. More generally, these results can be used to govern evaluation of thrust belts deforming over faulted basement, and to predict the locations of specific fault strands in a region where this information is unknown.
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Trexler, Charles C., Eric Cowgill, Nathan A. Niemi, Dylan A. Vasey, and Tea Godoladze. "Tectonostratigraphy and major structures of the Georgian Greater Caucasus: Implications for structural architecture, along-strike continuity, and orogen evolution." Geosphere 18, no. 1 (January 6, 2022): 211–40. http://dx.doi.org/10.1130/ges02385.1.
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Abstract Although the Greater Caucasus Mountains have played a central role in absorbing late Cenozoic convergence between the Arabian and Eurasian plates, the orogenic architecture and the ways in which it accommodates modern shortening remain debated. Here, we addressed this problem using geologic mapping along two transects across the southern half of the western Greater Caucasus to reveal a suite of regionally coherent stratigraphic packages that are juxtaposed across a series of thrust faults, which we call the North Georgia fault system. From south to north within this system, stratigraphically repeated ~5–10-km-thick thrust sheets show systematically increasing bedding dip angles (<30° in the south to subvertical in the core of the range). Likewise, exhumation depth increases toward the core of the range, based on low-temperature thermochronologic data and metamorphic grade of exposed rocks. In contrast, active shortening in the modern system is accommodated, at least in part, by thrust faults along the southern margin of the orogen. Facilitated by the North Georgia fault system, the western Greater Caucasus Mountains broadly behave as an in-sequence, southward-propagating imbricate thrust fan, with older faults within the range progressively abandoned and new structures forming to accommodate shortening as the thrust propagates southward. We suggest that the single-fault-centric “Main Caucasus thrust” paradigm is no longer appropriate, as it is a system of faults, the North Georgia fault system, that dominates the architecture of the western Greater Caucasus Mountains.
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FUENTES, FACUNDO, BRIAN K. HORTON, DANIEL STARCK, and ANDRÉS BOLL. "Structure and tectonic evolution of hybrid thick- and thin-skinned systems in the Malargüe fold–thrust belt, Neuquén basin, Argentina." Geological Magazine 153, no. 5-6 (July 25, 2016): 1066–84. http://dx.doi.org/10.1017/s0016756816000583.
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AbstractAndean Cenozoic shortening within the Malargüe fold–thrust belt of west-central Argentina has been dominated by basement faults largely influenced by pre-existing Mesozoic rift structures of the Neuquén basin system. The basement contractional structures, however, diverge from many classic inversion geometries in that they formed large hanging-wall anticlines with steeply dipping frontal forelimbs and structural relief in the order of several kilometres. During Cenozoic E–W shortening, the reactivated basement faults propagated into cover strata, feeding slip to shallow thrust systems that were later carried in piggyback fashion above newly formed basement structures, yielding complex thick- and thin-skinned structural relationships. In the adjacent foreland, Cenozoic clastic strata recorded the broad kinematic evolution of the fold–thrust belt. We present a set of structural cross-sections supported by regional surface maps and industry seismic and well data, along with new stratigraphic information for associated Neogene synorogenic foreland basin fill. Collectively, these results provide important constraints on the temporal and geometric linkages between the deeper basement faults (including both reactivated and newly formed structures) and shallow thin-skinned thrust systems, which, in turn, offer insights for the understanding of hydrocarbon systems in the actively explored Neuquén region of the Andean orogenic belt.
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Duvall, Alison R., Sarah A. Harbert, Phaedra Upton, Gregory E. Tucker, Rebecca M. Flowers, and Camille Collett. "River patterns reveal two stages of landscape evolution at an oblique convergent margin, Marlborough Fault System, New Zealand." Earth Surface Dynamics 8, no. 1 (February 28, 2020): 177–94. http://dx.doi.org/10.5194/esurf-8-177-2020.
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Abstract. Here we examine the landscape of New Zealand's Marlborough Fault System (MFS), where the Australian and Pacific plates obliquely collide, in order to study landscape evolution and the controls on fluvial patterns at a long-lived plate boundary. We present maps of drainage anomalies and channel steepness, as well as an analysis of the plan-view orientations of rivers and faults, and we find abundant evidence of structurally controlled drainage that we relate to a history of drainage capture and rearrangement in response to mountain-building and strike-slip faulting. Despite clear evidence of recent rearrangement of the western MFS drainage network, rivers in this region still flow parallel to older faults, rather than along orthogonal traces of younger, active strike-slip faults. Such drainage patterns emphasize the importance of river entrenchment, showing that once rivers establish themselves along a structural grain, their capture or avulsion becomes difficult, even when exposed to new weakening and tectonic strain. Continued flow along older faults may also indicate that the younger faults have not yet generated a fault damage zone with the material weakening needed to focus erosion and reorient rivers. Channel steepness is highest in the eastern MFS, in a zone centered on the Kaikōura ranges, including within the low-elevation valleys of main stem rivers and at tributaries near the coast. This pattern is consistent with an increase in rock uplift rate toward a subduction front that is locked on its southern end. Based on these results and a wealth of previous geologic studies, we propose two broad stages of landscape evolution over the last 25 million years of orogenesis. In the eastern MFS, Miocene folding above blind thrust faults generated prominent mountain peaks and formed major transverse rivers early in the plate collision history. A transition to Pliocene dextral strike-slip faulting and widespread uplift led to cycles of river channel offset, deflection and capture of tributaries draining across active faults, and headward erosion and captures by major transverse rivers within the western MFS. We predict a similar landscape will evolve south of the Hope Fault, as the locus of plate boundary deformation migrates southward into this region with time.
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Cheng, Feng, Andrew V. Zuza, Peter J. Haproff, Chen Wu, Christina Neudorf, Hong Chang, Xiangzhong Li, and Bing Li. "Accommodation of India–Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold–thrust belt, northern margin of the Tibetan Plateau." Journal of the Geological Society 178, no. 3 (January 29, 2021): jgs2020–207. http://dx.doi.org/10.1144/jgs2020-207.
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Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a−1, which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent.Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MNThematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts
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Minguely, Bruno, Olivier Averbuch, Marie Patin, David Rolin, Franck Hanot, and Francoise Bergerat. "Inversion tectonics at the northern margin of the Paris basin (northern France): new evidence from seismic profiles and boreholes interpolation in the Artois area." Bulletin de la Société Géologique de France 181, no. 5 (September 1, 2010): 429–42. http://dx.doi.org/10.2113/gssgfbull.181.5.429.
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AbstractA synthesis of existing borehole data and seismic profiles has been conducted in the Artois area (northern France), along the northern border of the Paris basin, in order to explore the possible control exerted at depth by the Upper Carboniferous Variscan thrust front on the distribution of Late Paleozoic-Mesozoic depositional centers and their subsequent uplift in Tertiary times. Such control was demonstrated recently in the Weald-Boulonnais basin (Eastern Channel area) that forms the western prolongation of the area under study but was so far poorly constrained in the Artois area. Presented data provide evidence for the topography of the Artois hills and the altitude of sedimentary layers to be controlled by the activity of a network of relaying WNW-ESE striking faults inducing the systematic uplift of the southern fault blocks. Those steeply S-dipping faults branch downward onto the ramp of the Variscan thrusts forming listric faults that locally limit to the north buried half-graben structures, filled with fan-shaped fluviatile Stephanian-Permian deposits. Such clear syn-rift geometry shows that the ramp of the main Variscan frontal thrust (the Midi thrust) has been reactivated as a normal fault in Stephanian-Permian times thus forming a very demonstrative example of a negative inversion process. The reverse offset of the transgressive Middle Cretaceous-Lower Eocene layers covering unconformably the Paleozoic substratum argue for a Tertiary (Middle Eocene-Late Oligocene?) contractional reactivation of the fault network thereby documenting a repeated inversion process along the Artois Variscan thrust front. The Variscan frontal thrust zone is thus shown here to represent a prominent crustal-scale mechanical discontinuity that localized deformation in the Artois-Boulonnais area since Upper Paleozoic times.
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Yaseen, Muhammad, Muhammad Shahab, Zeeshan Ahmad, Rehman Khan, Syed Farhan Ali Shah, and Abbas Ali Naseem. "Insights into the structure and surface geology of balanced and retrodeformed geological cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan." Journal of Petroleum Exploration and Production Technology 11, no. 6 (May 9, 2021): 2561–71. http://dx.doi.org/10.1007/s13202-021-01180-8.
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AbstractThe current research work is an attempt to apply the basic geological procedures, methods of geological mapping, surface and subsurface interpretation and restoration of balanced and retrodeformed cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan. The work also includes the documentation of several surface structural features, i.e., anticlines, synclines and different types of folds and faults exposed in the vicinity of study area. Four central thrust faults were recognized named as Kahi Thrusts along the cross sections. These thrust faults carried the older sequences of rocks over the younger sequences in different portion along the measured cross section. The folded and faulted rocks in the area show that stratigraphic framework comprises of Eocene, Paleocene, Cretaceous and Jurassic succession of rocks. There are Eocene rocks existing in the extreme South of the mapped area with addition of older Cretaceous and Jurassic succession and contains simple and large-scale folds, faults and back thrust. Two structural transect were mapped which encounter different folds and faults, i.e., X-sections AB oriented NS and CD oriented NE-SW. Restoration of the structural transects was calculated and assumed that at the formation of Main Boundary Thrust, the study area was exposed to the tectonic forces which prognosticated 19.5% shortening in rock sequences from Jurassic to Eocene succession along the measured cross section A_B.
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Alavi, Mehdi, and M. A. Mahdavi. "Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics." Geological Magazine 131, no. 1 (January 1994): 43–47. http://dx.doi.org/10.1017/s0016756800010475.
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AbstractSeveral rock stratigraphic successions, metamorphosed and non-metamorphosed, are found to be similar and/or identical with each other across the so-called ‘Main Zagros Thrust’. Stratigraphic successions form thin allochthonous sheets carried from northeast to southwest by numerous low-angle thrust faults of either ductile to brittle-ductile type or brittle type. Similarities in lithic and faunal characteristics of the stratigraphic units and in the style of structural deformation across the ‘Main Zagros Thrust’ imply that either the suture between the Afro-Arabian and Iranian lithospheric plates is not located in the Nahavand region or, if it is, it must be buried under several thrust sheets.
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NELSON, W. JOHN, and ROBERTA BAUER. "Thrust faults in southern Illinois basin—Result of contemporary stress?" Geological Society of America Bulletin 98, no. 3 (1987): 302. http://dx.doi.org/10.1130/0016-7606(1987)98<302:tfisib>2.0.co;2.
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Keller, J. V. A., and M. P. Coward. "The structure and evolution of the Northern Tyrrhenian Sea." Geological Magazine 133, no. 1 (January 1996): 1–16. http://dx.doi.org/10.1017/s0016756800007214.
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AbstractField studies on the island of Elba and seismic lines from the Northern Tyrrhenian Sea, Italy, indicate that major extensional displacements were accommodated along east-dipping low-angle detachment faults. The rifting and subsidence in the Northern Tyrrhenian Sea basin have followed convergence and collision of the Corso-Sardinian block and the Apulian microplate. This collisional episode produced the Northern Apennines fold-and-thrust belt. Major extensional faults cut down-section through the stratigraphy and pre-existing west-dipping thrust faults. West-dipping thrusts can also be reactivated and form antithetic faults to the east-dipping detachments. Brittle deformation conditions predominated during the extensional phase. The geometry, internal structure and the fabrics (brittle and penetrative) associated with a well-exposed low-angle extensional detachment in Elba are presented in this paper. A geometrical model for the brittle extensional faulting is presented in which regional extension was accommodated on a system consisting of two sets of simultaneously active antithetic faults. The east-dipping detachment faults appear to have started at steeper angles, based on field and seismic observations, and rotated counter-clockwise to lower dips. Due to this rotation, and for space accommodation, antithetic west-dipping faults formed and rotated clockwise. A tectonic model is proposed whereby slowing of the convergence between Apulia and Corsica, as well as Tethys oceanic crust and Apulian crust subduction, led to the delamination of the Apulian litho-spheric mantle away from the crust. Accompanying asthenospheric upwelling and intrusion at the crust—mantle interface beneath the Tyrrhenian Sea caused late orogenic crustal stretching in the Northern Apennines internal zone.
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Lacroix, Brice, Anna Travé, Martine Buatier, Pierre Labaume, Torsten Vennemann, and Michel Dubois. "Syntectonic fluid-flow along thrust faults: Example of the South-Pyrenean fold-and-thrust belt." Marine and Petroleum Geology 49 (January 2014): 84–98. http://dx.doi.org/10.1016/j.marpetgeo.2013.09.005.
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Schmidt, William L., and John P. Platt. "Metamorphic Temperatures and Pressures across the Eastern Franciscan: Implications for Underplating and Exhumation." Lithosphere 2020, no. 1 (November 9, 2020): 1–19. http://dx.doi.org/10.2113/2020/8853351.
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Abstract The Eastern Belt of the Franciscan Complex in the northern California Coast Ranges consists of coherent thrust sheets predominately made up of ocean floor sediments subducted in the Early Cretaceous and then accreted to the overriding plate at depths of 25-40 km. Progressive packet accretion resulted in the juxtaposition of a series of thrust sheets of differing metamorphic grades. This study utilizes laser Raman analysis of carbonaceous material to determine peak metamorphic temperatures across the Eastern Belt and phengite barometry to determine peak metamorphic pressures. Locating faults that separate packets in the field is difficult, but they can be accurately located based on differences in peak metamorphic temperature revealed by Raman analysis. The Taliaferro Metamorphic Complex in the west reached 323-336°C at a minimum pressure of ~11 kbar; the surrounding Yolla Bolly Unit 215–290°C; the Valentine Springs Unit 282-288°C at 7.8±0.7 kbar; the South Fork Mountain Schist 314–349°C at 8.6–9.5 kbar, a thin slice in the eastern portion of the SFMS, identified here for the first time, was metamorphosed at ~365°C and 9.7±0.7 kbar; and a slice attributed to the Galice Formation of the Western Klamath Mountains at 281±13°C. Temperatures in the Yolla Bolly Unit and Galice slice were too low for the application of phengite barometry. Microfossil fragments in the South Fork Mountain Schist are smaller and less abundant than in the underlying Valentine Springs Unit, providing an additional method of identifying the boundary between the two units. Faults that record a temperature difference across them were active after peak metamorphism while faults that do not were active prior to peak metamorphism, allowing for the location of packet bounding faults at the time of accretion. The South Fork Mountain Schist consists of two accreted packets with thicknesses of 300 m and 3.5 km. The existence of imbricate thrust faults both with and without differences in peak metamorphic temperature across them provides evidence for synconvergent exhumation.
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SOTIROPOULOS, SPILIOS, EVANGELOS KAMBERIS, MARIA V. TRIANTAPHYLLOU, and THEODOR DOUTSOS. "Thrust sequences in the central part of the External Hellenides." Geological Magazine 140, no. 6 (November 2003): 661–68. http://dx.doi.org/10.1017/s0016756803008367.
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The model of a foreland propagating sequence already presented for the External Hellenides is significantly modified in this paper. New data are used, including structural maps, cross-sections, stratigraphic determinations and seismic profiles. In general, thrusts formed a foreland propagating sequence but they acted simultaneously for a long period of time. Thus, during the Middle Eocene the Pindos thrust resulted in the formation of the Ionian–Gavrovo foreland and acted in tandem with the newly formed Gavrovo thrust within the basin until the Late Oligocene. The Gavrovo thrust consists of segments, showing that out-of-sequence thrusting was important. Thrust nucleation and propagation history is strongly influenced by normal faults formed in the forebulge region of the Ionian–Gavrovo foreland basin. Shortening rates within the Gavrovo–Ionian foreland are low, about 1 mm/year. Although thrust load played an important role in the formation of this basin, the additional load of 3500 m thick clastics in the basin enhanced subsidence and underthrusting.
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Ahmed, Mustafa, Thair Al-Samarrai, and Suhail Muhsin. "Study of Subsurface Structural Image and Model Using 2D Seismic Reflection Method of Injana Field Area, Northeastern Iraq." Iraqi Geological Journal 55, no. 1E (May 31, 2022): 64–73. http://dx.doi.org/10.46717/igj.55.1e.6ms-2022-05-22.
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The Injana field area is located to the north of Baquba city within Diyala. which was studied and interpreted by using 2D seismic data from the Oil Exploration Company. The study was concerned with the Jeribe Formation which is located within the Injana field area and belongs to the Tertiary Age. Two reflectors were detected based on synthetic seismograms and well logs of the Khashim Al-Ahmer-2 well. The structural maps were derived from seismic reflection interpretations to determine the location and direction of the basin. The depth maps were conducted depending upon the structural interpretation of the picked reflectors to show several structural features. Structurally, seismic sections show that the Injana area is affected by two types of reverse fault systems trending in a NW-SE direction, the first represents thrust faults affected on the lower Fars (Red Beds & Seepage) and the layers above it, the salt bed within Lower Fars Formation being as a detachment surface of this fault, the second represents two reverse faults affected on the bottom part of the Lower Fars (Transition beds) and the layers beneath. In addition, the reverse faults become dense in the north part. The structural maps reveal an elongated asymmetrical narrow anticline affected by one major thrust fault at Lower Fars Formation, and an elongated asymmetrical narrow anticline surrounded by two major reverse faults and consisting of three domes separated, Injana, Khashim Al-Ahmer and Khashab domes at the Jeribe Formation.
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Kawamura, Kiichiro, and Yujiro Ogawa. "Internal structure, active tectonics and dynamic topography of the eastern Nankai accretionary prism toe, Japan, and its tsunamigenic potential." Geological Magazine 158, no. 1 (October 30, 2018): 30–38. http://dx.doi.org/10.1017/s0016756818000699.
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AbstractThe eastern Nankai accretionary prism toe was surveyed to evaluate the nature and deformation of its frontal thrust. According to the determined porosities and yield strengths, turbidites were successively buried down to depths of 250–300 m before accretion, and were then exposed at the prism toe by uplift along the Tenryu frontal thrust during 3.4–1.98 Ma. Consolidation tests provided reasonable estimates of burial depth and, when combined with exposed sediment dates, yield prism toe uplift rates of 0.74–2.27 m ka–1. The displacement along the frontal thrust is estimated to be 500–900 m and the slip rates are 1.47–4.55 m ka–1, corresponding to the highest class of active faults on land in Japan. During the surveys of the Tenryu frontal thrust zone, we discovered a new active fault scarp that was several tens of centimetres high, interpreted to be a protothrust located c. 100 m south of the frontal thrust. This scarp is associated with chemosynthetic biocommunities. The thrust might potentially be the result of displacement during the East Nankai (To-Nankai) earthquake (Mw 8.1) in 1944. These lines of evidence indicate that the Tenryu frontal thrust is still active and that displacement along the thrust might induce a tsunami during future Tokai or To-Nankai earthquakes.
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Cruset, D., J. Vergés, R. Albert, A. Gerdes, A. Benedicto, I. Cantarero, and A. Travé. "Quantifying deformation processes in the SE Pyrenees using U–Pb dating of fracture-filling calcites." Journal of the Geological Society 177, no. 6 (August 4, 2020): 1186–96. http://dx.doi.org/10.1144/jgs2020-014.
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It is difficult to quantify the timing of the deformation processes in brittle fold–thrust belts because minerals suitable for dating and well-preserved growth strata sediments are scarce or absent. Here, we quantify the duration of thrust sheet emplacement and shortening rates in the SE Pyrenean thrust sequence using U–Pb dating of fracture-filling calcites. The obtained U–Pb dates reveal a minimum duration for the emplacement of each thrust unit (18.7 Ma for the Bóixols–Upper Pedraforca, 11.6 Ma for the Lower Pedraforca and 14.3 Ma for the Cadí thrust sheets) and show that piggy-back thrusting was accompanied by post-emplacement deformation of the upper thrust sheets above the lower sheets during their south-directed tectonic transport. We calculated shortening rates of 0.6, 3.1 and 1.1 mm a−1 from the older to younger emplaced thrust sheets. Our results also reveal the formation of local normal faults during the late Oligocene as a result of the late stages of compression and exhumation in the SE Pyrenees. We observed that temperatures >110 °C could be a limiting factor when applying the U–Pb dating method.Supplementary material: U-Pb analytical results, concordia plots and fracture data are available at https://doi.org/10.6084/m9.figshare.c.5078862
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White, Shawna E., and John W. F. Waldron. "Inversion of Taconian extensional structures during Paleozoic orogenesis in western Newfoundland." Geological Society, London, Special Publications 470, no. 1 (June 6, 2018): 311–36. http://dx.doi.org/10.1144/sp470.17.
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AbstractWest Newfoundland was critical in developing the Wilson Cycle concept. Neoproterozoic rifting established a passive margin adjacent to the Iapetus Ocean. Ordovician (Taconian) arc–continent collision emplaced ophiolites and the thin-skinned Humber Arm Allochthon. Subsequent Devonian (Acadian) ocean closure produced basement-cutting thrust faults that control the present-day distribution of units. New mapping, and aeromagnetic and seismic interpretation, around Parsons Pond enabled the recognition of structures in poorly exposed areas.Following Cambrian to Middle Ordovician passive-margin deposition, Taconian deformation produced a flexural bulge unconformity. Subsequent extensional faults shed localized conglomerate into the foreland basin. The Humber Arm Allochthon contains a series of stacked and folded duplexes, typical of thrust belts. To the east, the Parsons Pond Thrust has transported shelf and foreland-basin units c. 8 km westwards above the allochthon. The Long Range Thrust shows major topographical expression but <1 km offset. Stratigraphic relationships indicate that most thrusts originated as normal faults, active during Neoproterozoic rifting, and subsequently during Taconian flexure. Devonian continental collision inverted the Parsons Pond and Long Range thrusts. Basement-cored fault-propagation folds in Newfoundland are structurally analogous to basement uplifts in other orogens, including the Laramide Orogen in western USA. Similar deep-seated inversion structures may extend through the northern Appalachians.
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Delteil, Jean, Jean-François Stephan, and Mikaël Attal. "Control of Permian and Triassic faults on Alpine basement deformation in the Argentera massif (external southern French Alps)." Bulletin de la Société Géologique de France 174, no. 5 (September 1, 2003): 481–96. http://dx.doi.org/10.2113/174.5.481.
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Abstract Structural investigations reveal intense and heterogeneous deformation of the sedimentary cover attached to the basement complex of the southern Argentera and Barrot massifs (southernmost External Basement Massifs of the French Alps). Permian and early Triassic syn-depositional extensional tectonics imparted a tilted block pattern to the massifs. An early Miocene first stage of Alpine compression caused pervasive cleavage. This cleavage was controlled by the former pre-existing faults but is nevertheless consistent with NNE contraction. Where regional shortening is orthogonal to the trend of pre-existing faults the pervasive deformation produced either irrotational compressional strain (where no fault inversion occurred), or rotational compressional strain involving syn-cleavage shearing (where faults with favorable paleo-dip were inverted). Where the shortening direction is oblique to the paleo-fault trends, a component of strike-slip movement may locally prevail. A 22 %, N020o directed horizontal shortening, of 11 km, has been calculated based on deformed sedimentary markers in the Permian series and parallel folds in Lower Triassic quartzite. A shallower deformation as brittle reverse faults postdates the cleavage at the southwestern tip of the Argentera Massif and accounts for 4 km of extra shortening. Both types of deformation are connected at depth to a crustal blind thrust system and the Argentera Massif is over-thrust to the south-southwest. The observed strain indicates the Argentera Massif area underwent, from earliest Miocene to Present, a NNE to N rotating compression at distance from the left-lateral southwestern boundary of the Adria block.
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Rowan, Mark G., Josep Anton Muñoz, Eduard Roca, Oriol Ferrer, Pablo Santolaria, Pablo Granado, and Marco Snidero. "Linked detachment folds, thrust faults, and salt diapirs: Observations and analog models." Journal of Structural Geology 155 (February 2022): 104509. http://dx.doi.org/10.1016/j.jsg.2022.104509.
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Watkinson, A. J. "A footwall system of faults associated with a foreland thrust in Montana." Journal of Structural Geology 15, no. 3-5 (March 1993): 335–42. http://dx.doi.org/10.1016/0191-8141(93)90130-3.
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McNab, Fergus, R. Alastair Sloan, and Richard T. Walker. "Simultaneous orthogonal shortening in the Afghan-Tajik Depression." Geology 47, no. 9 (July 16, 2019): 862–66. http://dx.doi.org/10.1130/g46090.1.
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Abstract The Afghan-Tajik Depression is a sedimentary basin in the Alpine-Himalayan mountain chain. It is traversed by series of north-south arcuate folds, suggesting that the basin is undergoing east-west compression. A second set of folds in the south of the depression runs east-west, crosscutting those trending north-south. We present results from teleseismic body waveform inversion and depth phase modeling for five recent earthquakes, and from detailed mapping of structures related to active faulting based on satellite imagery and topographic data. We argue that both sets of folds are active and that deformation is vertically partitioned, with north-south compression accommodated on east-west–trending thrust faults within the basement, and east-west compression accommodated on north-south–trending thrust faults above a detachment within the basin fill. The observation that orthogonal shortening can be accommodated simultaneously in this way has several important implications. Juxtaposed orthogonal fold systems identified in the geological record may not require temporally separate events, particularly in gravity-driven fold-and-thrust belts in foreland-basin settings. Pervasive detachment may limit the size of potential earthquakes by preventing single events from rupturing the entire seismogenic layer. However, it may also disguise geomorphic signatures of faulting and interseismic strain accumulation within the lower layer, hindering accurate seismic hazard assessment and regional tectonic interpretations.
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Hervouet, Yves, Jose Tomass Castrillo-Delgado, and Oscar Odreman. "Interaction entre un chevauchement imbrique et une zone transcurrente; le flanc nord-ouest de Andes venezueliennes." Bulletin de la Société Géologique de France 172, no. 2 (March 1, 2001): 159–75. http://dx.doi.org/10.2113/172.2.159.
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Abstract Geological framework; Geological setting: The Venezuela Andes or Merida Andes (fig. 1) extend from the Colombian border in the SW to Barquisimeto in the NE, and constitute a basement uplift exceeding 5,000 m near Merida (Pico Bolivar). This young chain is bordered to the W by the Maracaibo foredeep basin, and to the E by the Barinas-Apure foreland basin. The Bocono fault divides the Andean Belt in two parts along a NE-SW direction. This shows that the uplift of the Andes is contemporaneous with an oblique translation. In the study area, located on the northwestern flank near Maracaibo basin, three major structures are present: in the E, the N-S senestral strike slip Valera-Rio Momboy fault, in the S the E-W dextral strike slip Pinango fault and, in the center, the SW-NE striking Las Virtudes thrust verging toward NW. Lithologic and stratigraphic formations (fig. 4): The Las Virtudes Fault separates two different structural zones. In the SE, overthrust units are made of crystalline basement, Paleozoic substratum and preorogenic sedimentary formations (Cretaceous-Eocene). The foredeep flexural basin, located NW, is filled by synorogenic molasses (Neogene and Quaternary), largely developed within the Betijoque Fm. (Upper Miocene to Pliocene in age) which reaches a thickness of 5000 m. Structure of the northwestern Andean flank; Las Virtudes Fault and its thrust slice zone: Near Las Virtudes village (fig. 5, 6-2), this thrust is systematically associated with a narrow overturned foredeep depobelt (Cretaceous to Neogene in age). These slices are unknown elsewhere in the Andean Chain and represent the terminal faulted part of the thrust drag. However, where this slice zone is missing (central and northeastern part of the study area), the Las Virtudes Fault is not clearly documented: its throw decreases rapidly and it is possible that the fault disappears northeastward. Andean unit: Near the main strike slip faults, NE trending SE verging reverse faults develop (fig. 6-5). In central and northeastern parts, the throw of the reverse faults increases toward the Valera Fault. It seems that reverse faults are horsetail of this major strike slip fault (fig. 5). Internal part of the northwestern Andean foredeep basin: The foredeep sedimentary formations generally dip toward the NW. Associated to the lack of some formations, tilted anticlines toward the SE are observed (fig. 6-3 and 6-7), and indicate the vicinity of decollement levels in the foredeep, located in Luna-Colon, Pauji and Betijoque Fm.. Seismic profiles show (fig. 7) that the major decollement level of the foredeep is located in La Luna and Colon Fms. [Audemard, 1991; De Toni and Kellogg, 1993; Colletta et al., 1997]. Crustal architecture and timing of the deformation: Several stages can be distinguished in the building of the Andes. Development of an intracutaneous thrust wedge: The first effects of the Andean phase during Miocene are the development of an intracutaneous thrust wedge [Price, 1986]. The lower flat is located in the basement and the upper one in Cretaceous formations. The transport direction is NW. The foredeep develops on the forelimb of this structure and collects detrital products coming from erosion of the first (oldest) reliefs. Decollements in the foredeep basin could be contemporaneous with this major overthrust. Their origin could be due to radius of curvature differences within the thick sedimentary formations (fig. 8). Las Virtudes Fault and backthrusting: Las Virtudes Fault is one of the last events of this part of the Andean Belt. During Plio-Pleistocene, the continental crust breaks with a dip of 35 degrees SE. The Andean unit overthrusts the foredeep basin. Some of the foredeep decollements could still be active and form, together with Andean basement, a triangle zone. Las Virtudes Fault throw reaches 5 km between Las Virtudes and Monte Carmelo villages (fig. 8A). It decreases southwestwards and the back thrusts are probably younger. Northeastwards the throw decreases and eventually disappears (fig. 8B). In the same time the back thrust throws increase. Both seem to be contemporaneous. Conclusions: This structural model explains the basement occurrence in front of the Las Virtudes Fault on seismic profiles and allows to restore correctly the different northwestern flank structures of the Venezuela Andes. These structures can be explained by the conjugate movements of a NW verging intracutaneous thrust wedge and strike slip faults which create a SE verging triangular area (fig. 5). The Andean overthrust is transferred in the Falcon zone along the Valera fault. In the northeastern part of the Maracaibo block, the Valera and Bocono strike slip faults limit the Trujillo block (fig. 10) which moves towards the North during Neogene and Quaternary times.
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Levy, Y., T. K. Rockwell, J. H. Shaw, A. Plesch, N. W. Driscoll, and H. Perea. "Structural modeling of the Western Transverse Ranges: An imbricated thrust ramp architecture." Lithosphere 11, no. 6 (November 4, 2019): 868–83. http://dx.doi.org/10.1130/l1124.1.
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Abstract Active fold-and-thrust belts can potentially accommodate large-magnitude earthquakes, so understanding the structure in such regions has both societal and scientific importance. Recent studies have provided evidence for large earthquakes in the Western Transverse Ranges of California, USA. However, the diverse set of conflicting structural models for this region highlights the lack of understanding of the subsurface geometry of faults. A more robust structural model is required to assess the seismic hazard of the Western Transverse Ranges. Toward this goal, we developed a forward structural model using Trishear in MOVE® to match the first-order structure of the Western Transverse Ranges, as inferred from surface geology, subsurface well control, and seismic stratigraphy. We incorporated the full range of geologic observations, including vertical motions from uplifted fluvial and marine terraces, as constraints on our kinematic forward modeling. Using fault-related folding methods, we predicted the geometry and sense of slip of the major faults at depth, and we used these structures to model the evolution of the Western Transverse Ranges since the late Pliocene. The model predictions are in good agreement with the observed geology. Our results suggest that the Western Transverse Ranges comprises a southward-verging imbricate thrust system, with the dominant faults dipping as a ramp to the north and steepening as they shoal from ∼16°–30° at depth to ∼45°–60° near the surface. We estimate ∼21 km of total shortening since the Pliocene in the eastern part of the region, and a decrease of total shortening west of Santa Barbara down to 7 km near Point Conception. The potential surface area of the inferred deep thrust ramp is up to 6000 km2, which is of sufficient size to host the large earthquakes inferred from paleoseismic studies in this region.
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Aagaard, Brad T., John F. Hall, and Thomas H. Heaton. "Characterization of Near-Source Ground Motions with Earthquake Simulations." Earthquake Spectra 17, no. 2 (May 2001): 177–207. http://dx.doi.org/10.1193/1.1586171.
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We examine the characteristics of long-period near-source ground motions by conducting a sensitivity study with variations in six earthquake source parameters for both a strike-slip fault ( M 7.0-7.1) and a thrust fault ( M 6.6-7.0). The directivity of the ruptures creates large displacement and velocity pulses in the forward direction. The dynamic displacements close to the fault are comparable to the average slip. The ground motions exhibit the greatest sensitivity to the fault depth with moderate sensitivity to the rupture speed, peak slip rate, and average slip. For strike-slip faults and thrust faults with surface rupture, the maximum ground displacements and velocities occur in the region where the near-source factor from the 1997 Uniform Building Code is the largest. However, for a buried thrust fault the peak ground motions can occur up-dip from this region.
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Koukouvelas, I., G. Pe-Piper, and D. J. W. Piper. "Pluton emplacement by wall-rock thrusting, hanging-wall translation and extensional collapse: latest Devonian plutons of the Cobequid fault zone, Nova Scotia, Canada." Geological Magazine 133, no. 3 (May 1996): 285–98. http://dx.doi.org/10.1017/s001675680000902x.
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AbstractLatest Devonian A-type granite-gabbro plutons, in part ductilely deformed, are spatially associated with the strike-slip Cobequid fault zone. The youngest intrusions are close to the Cobequid fault zone, which was the main conduit for magma. Two phases of deformation accompanying magma emplacement are recognized. Early magmas intruded ductile rocks during left-lateral oblique thrust movements. A second stage of right-lateral oblique slip normal faulting accommodated uplift of the plutons when coarse granite was emplaced in the crestal regions. Cross-cutting late stage porphyries, granitic clasts in marginal basins cut by granitic dykes, and superposition of brittle on ductile structures all indicate rapid uplift of the plutons. The geometry of the Cobequid fault zone shows that pluton emplacement was not the result of extension in releasing bends during transcurrent shear. Rather, flower-structure high-angle faults acted as magma conduits and space was created by two processes: translation of wall rocks along thrust faults at depth, developing space away from the master fault zone and backward collapse of the uplifted magma chamber creating space towards the fault zone.
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Martin, C. D. "Characterizing in situ stress domains at the AECL Underground Research Laboratory." Canadian Geotechnical Journal 27, no. 5 (October 1, 1990): 631–46. http://dx.doi.org/10.1139/t90-077.
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The Underground Research Laboratory access shaft was excavated from the surface to about the 185 m depth in jointed pink granite. Below this depth to the 443 m depth the shaft was excavated in massive grey granite. The grey granite is essentially unjointed, except for a major low-dipping thrust fault and associated minor splays. Overcoring, hydraulic fracturing, convergence measurements, microseismic monitoring, and observations of shaft-wall failure and core discing indicate that unusually high in situ stresses can be associated with large volumes of massive, unjointed granite at fairly shallow depth. The database of in situ stress measurements collected at the Underground Research Laboratory indicates that major geological features, such as thrust faults, can act as boundaries for in situ stress domains and that both the magnitude and direction of the in situ stress state can change when these geological features are traversed. Key words: in situ stress, anisotropy, stress domains, thrust faults, overcoring, hydraulic fracturing, convergence measurements, excavation damage zones.
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Noweir, M. Atef, and Abdulrahman S. Alsharhan. "Structural Style and Stratigraphy of the Huwayyah Anticline: an Example of an Al-Ain Tertiary Fold, Northern Oman Mountains." GeoArabia 5, no. 3 (July 1, 2000): 387–402. http://dx.doi.org/10.2113/geoarabia0503387.
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ABSTRACT Detailed field mapping and structural studies in the Jebel Auha-Jebel Huwayyah area northeast of Al-Ain indicate that folding of neoautochthonous sedimentary rocks produced the north-northwest-trending Huwayyah Anticline. The anticline at the surface is composed of the Maastrichtian Qahlah and Simsima formations unconformably overlain by shallow-marine carbonate rocks that are correlated on faunal grounds with the Middle Eocene Dammam Formation. The investigation of the Huwayyah Anticline has identified three microfacies of bioclastic packstone, nummulitic packstone, and nummulitic packstone-grainstone in the local Dammam Formation. Diagenesis in the form of silicification, cementation, recrystallization, dissolution, compaction and neomorphism is widespread. The Huwayyah Anticline is a fault-propagation fold above a thrust ramp. The ramp developed from a pre-existing Late Cretaceous basal thrust within the Semail Ophiolite on the Oman Mountain Front. The anticline was formed as a result of regional compressive deformation due to rejuvenation of the Late Cretaceous thrust in post-Middle Eocene times. Westward-directed high-angle reverse faults of Jebel Auha trend parallel to the fold axis of the anticline. The Auha faults probably originated as west-dipping thrusts on the western flank of the anticline and were subsequently rotated to their present attitude as the flank of the anticline became steeper due to compression from the east.
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Fagereng, Å., H. M. Savage, J. K. Morgan, M. Wang, F. Meneghini, P. M. Barnes, R. Bell, et al. "Mixed deformation styles observed on a shallow subduction thrust, Hikurangi margin, New Zealand." Geology 47, no. 9 (July 16, 2019): 872–76. http://dx.doi.org/10.1130/g46367.1.
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Abstract Geophysical observations show spatial and temporal variations in fault slip style on shallow subduction thrust faults, but geological signatures and underlying deformation processes remain poorly understood. International Ocean Discovery Program (IODP) Expeditions 372 and 375 investigated New Zealand’s Hikurangi margin in a region that has experienced both tsunami earthquakes and repeated slow-slip events. We report direct observations from cores that sampled the active Pāpaku splay fault at 304 m below the seafloor. This fault roots into the plate interface and comprises an 18-m-thick main fault underlain by ∼30 m of less intensely deformed footwall and an ∼10-m-thick subsidiary fault above undeformed footwall. Fault zone structures include breccias, folds, and asymmetric clasts within transposed and/or dismembered, relatively homogeneous, silty hemipelagic sediments. The data demonstrate that the fault has experienced both ductile and brittle deformation. This structural variation indicates that a range of local slip speeds can occur along shallow faults, and they are controlled by temporal, potentially far-field, changes in strain rate or effective stress.
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Imrecke, Daniel B., Alexander C. Robinson, Lewis A. Owen, Jie Chen, Lindsay M. Schoenbohm, Kathryn A. Hedrick, Thomas J. Lapen, Wenqiao Li, and Zhaode Yuan. "Mesozoic evolution of the eastern Pamir." Lithosphere 11, no. 4 (May 16, 2019): 560–80. http://dx.doi.org/10.1130/l1017.1.
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Abstract We present field and analytical results from the Tashkurgan and Waqia valleys in the southeastern Pamir that shed new light on the tectonic evolution and terrane architecture of the region. Field mapping of metasedimentary and igneous units along the Tashkurgan and Waqia valleys in the Southeast Pamir, integrated with metamorphic petrology, garnet-biotite thermometry, and zircon U/Pb isotopic analysis, help identify major structures and terrane boundaries in the region, as well as compare structural units across the Miocene Muztaghata gneiss dome. South of the Muztaghata dome, the gently northwest-plunging synformal Torbashi thrust klippe juxtaposes amphibolite facies Triassic Karakul-Mazar terrane schist and gneiss structurally above (1) greenschist facies Triassic Karakul-Mazar terrane metasedimentary rock in the north, and (2) lower-amphibolite facies schist in the south that are interpreted to be Gondwanan-derived crust (Central or South Pamir terrane). Farther south, the Rouluke thrust fault imbricates the Gondwanan crust, placing early Paleozoic schists over Permian marble and slate. Exposure of the Torbashi thrust sheet terminates in the southeast, and with it the surface exposure of the Triassic Karakul-Mazar terrane, leaving the Paleozoic Kunlun terrane juxtaposed directly against Gondwanan terrane crust. Based on lithologic and isotopic similarities of units north and south of the Muztaghata gneiss dome, we document the existence of a regionally extensive thrust nappe that stretched across the northern and eastern Pamir, prior to being cut by Miocene exhumation of the Muztaghata dome. The thrust nappe links the Torbashi thrust in the southeast Pamir with the Tanymas thrust in the northern Pamir, and documents regionally extensive exposure of lithologically continuous units across the northeast Pamir. While timing of emplacement of the Torbashi thrust klippe and displacement on the Rouluke fault to the south is not well constrained, we interpret shortening to be Cretaceous in age based on previously published cooling ages. However, a component of Cenozoic shortening cannot be ruled out. A key observation from our mapping results is that the surface exposures of the Karakul–Mazar–Songpan Ganzi terrane are not continuous between western Tibet and the Pamir, which indicates tectonic and/or erosional removal, likely sometime in the Mesozoic. Furthermore, our documentation of the Jinsha suture in the southeast Pamir on the eastern side of the Karakoram fault shows deflections of terranes across the Himalayan-Tibetan orogen were not primarily accommodated along discrete, large displacement faults (>400 km) faults. Instead, oroclinal bending of the northern Pamir, and dextral shear along the Pamir margins, may be largely responsible for the northward deflection of terranes.
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Gestain, Vincent, Thierry Nalpas, Delphine Rouby, and Laurie Barrier. "Role of synkinematic ductile levels on the evolution of compressive zones – analogue modelling." Bulletin de la Société Géologique de France 175, no. 4 (July 1, 2004): 351–59. http://dx.doi.org/10.2113/175.4.351.
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Abstract In foldbelt faults, layers with ductile behaviour can form levels of décollement [Byerlee, 1978]. When these levels are prekinematic, they play a significant role in the genesis, evolution and final geometry of the foldbelt faults, as, for example in the Appalachian Mountains [Davis and Engelder, 1985], the Jura [Sommaruga, 1999], or the Pyrenees [Vergés et al., 1992]. Previous studies based on analogue modelling have shown how a prekinematic décollement level can influence the geometry of foldbelt faults and structures [Ballard, 1989; Colletta et al., 1991; Letouzey et al., 1995; Merle et Abidi, 1995]. However, no study has yet described the influence of synkinematic sedimentation of incompetent levels on the genesis and evolution of compressive structures. The laboratory experiments presented here are designed to explore some of the mechanisms of formation of synsedimentary thrust faults, in relation with the occurrence of a décollement layer during syntectonic sedimentation. Analogue modelling – Experimental procedure The models presented here were designed to simulate geological situations comparable to those observed on the border of an overthrust belt. The modelling techniques are similar to those usually applied in experiments on brittle-ductile systems at the Laboratory of Experimental Tectonics of the Geosciences department (Rennes University), and have been fully described in previous studies [e.g. Faugère and Brun, 1984; Vendeville et al., 1987; Davy and Cobbold, 1991]. The prekinematic and synkinematic brittle levels are represented by sand, while the prekinematic and synkinematic ductile levels are represented by silicone. The experimental apparatus is composed of a fixed and rigid basal plate over which a thin mobile plate is pushed at a constant rate. During shortening (of 5 cm), brittle sedimentation is simulated by sprinkling fresh sand onto the model, and ductile sedimentation is simulated by the deposition of a thin silicone plate onto the model. Photographs of the model surface are taken at regular time intervals to study the development of the structures. The internal structure is recorded from serial cross-sections cut after the experiments. The parameters tested are the sedimentation rate [see also Tondji Biyo, 1995; Nalpas et al., 1999; Barrier et al., 2002], and the presence and location of a synkinematic décollement layer. The sedimentation is homogeneously distributed on both sides of the relief developed above the thrust front, with a variable ratio R between the rate of sedimentation (vsed) and the rate of uplift (vup), with R taking the values (1) R = vsed/vup = 1/2, (2) R = 1 and (3) R = 2 [Barrier et al., 2002]. The décollement level is deposited at the beginning of sedimentation, either over the whole model or in front of the thrust throughout sedimentation. Results In all models, the progressive shortening is accommodated by two conjugate reverse faults. The major fault is antithetic to the displacement of the mobile wall. The synthetic fault is transitory [Ballard, 1989; Tondji Biyo, 1995]. In experiments without ductile sedimentation, the main thrust zone shows an increasing dip with each depositional increment [Barrier et al., 2002]. When the ductile level is deposited, (1) the dip of the main thrust decreases as it reaches the silicone, (2) a wedge of sand then penetrates the silicone forming a detachment, and (3) this wedge is abandoned and the main thrust fault cuts through the wedge, allowing the fault to propagate upward. At low sedimentation rate, the final geometry shows a major reverse fault made up of a ramp in the prekinematic sand and a flat in the synkinematic silicone. At high sedimentation rate, the major reverse fault is made up of a ramp in the prekinematic sand and a flat in the synkinematic silicone forming a distinctive wedge of sand and a prolongation of the ramp rear the sand wedge. The presence of a synkinematic ductile level in the model at the beginning of shortening favours decoupling between the prekinematic and the synkinematic sand: the faults in the prekinematic sand are not directly connected to the faults in the synkinematic sand. In addition, the deformation of the sand is different according to whether it is underneath or above the synkinematic ductile level. The prekinematic or synkinematic sand under the synkinematic ductile level is undeformed, whereas the synkinematic sand overlying the synkinematic ductile level is folded. Discussion In the presence of a ductile level, the reverse fault forms a flat in the silicone. The silicone leads to different behaviours of the fault and the synkinematic sand. This raises the question of how to identify synkinematic deposits in compressive basins. In most cases, only the geometry of the strata is used: if progressive unconformity is observed, the strata are synkinematic (growth strata), if not, the strata are deposited before or after the deformation. However, the evolution of growth-strata geometry is also related to the rheology of the rocks. Since geometrical criteria are insufficient, it is also necessary to take account of facies variations. Conclusions The presence of a synkinematic ductile level results in the development of a low angle thrust. The presence of synkinematic ductile levels facilitates deformation and the development of progressive unconformity in growth strata. Synkinematic sediments with brittle behaviour, deposited in front of a thrust fault, cannot develop a progressive unconformity. The absence of a progressive unconformity does not necessarily rule out a formation being synkinematic.
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Carlsen, G. M., A. P. Simeonova, and S. N. Apak. "PETROLEUM SYSTEMS AND EXPLORATION POTENTIAL IN THE OFFICER BASIN, WESTERN AUSTRALIA." APPEA Journal 43, no. 1 (2003): 473. http://dx.doi.org/10.1071/aj02025.
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The Officer Basin in Western Australia contains a variety of hydrocarbon plays associated with compressional, halokinetic, unconformity and stratigraphic traps. Five distinct structural zones have been defined in the basin—a northeastern Marginal Overthrusted Zone, a northeastern Salt-ruptured Zone, a central Thrusted Zone, a Western Platform and a complex salt-dominated Minibasins Zone. These zones, together with salt-associated and sub-salt structure, are well delineated on about 2,900 km of reprocessed 1980s vintage seismic data, now publicly released.Neoproterozoic rocks are marginally to fully mature for oil generation on the Western Platform and immature to overmature for different levels of the succession in the Salt-ruptured and Thrusted zones. Geochemical modelling indicates that the main phases of oil generation vary from different stratigraphic intervals and different parts of the Neoproterozoic basin with peaks during the latest Neoproterozoic, Cambrian, and Permian–Triassic. A variety of hydrocarbon shows have been recorded in each of the structural zones. The most recent, a gas show recorded in the stratigraphic well Vines–1 indicates the presence of potentially effective petroleum systems in the unexplored Waigen area of the Marginal Overthrusted Zone.A wide variety of trap styles have been identified, associated with normal faults, thrust faults, thrust ramp folds, compressive folds, fault tip folds, sub-salt plays, unconformity truncations, pinchouts, lateral facies changes, erosive channels and valleys, fractured carbonates and halokinetic traps. Most of these trap styles are poorly tested or untested.
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Stockmal, Glen S., Art Slingsby, and John W. F. Waldron. "Basement-involved inversion at the Appalachian structural front, western Newfoundland: an interpretation of seismic reflection data with implications for petroleum prospectivity." Bulletin of Canadian Petroleum Geology 52, no. 3 (September 1, 2004): 215–33. http://dx.doi.org/10.2113/52.3.215.
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Abstract Recent hydrocarbon exploration in western Newfoundland has resulted in six new wells in the Port au Port Peninsula area. Port au Port No.1, drilled in 1994/95, penetrated the Cambro-Ordovician platform and underlying Grenville basement in the hanging wall of the southeast-dipping Round Head Thrust, terminated in the platform succession in the footwall of this basement-involved inversion structure, and discovered the Garden Hill petroleum pool. The most recent well, Shoal Point K-39, was drilled in 1999 to test a model in which the Round Head Thrust loses reverse displacement to the northeast, eventually becoming a normal fault. This model hinged on an interpretation of a seismic reflection survey acquired in 1996 in Port au Port Bay. This survey is now in the public domain. In our interpretation of these data, the Round Head Thrust is associated with another basement-involved feature, the northwest-dipping Piccadilly Bay Fault, which is mapped on Port au Port Peninsula. Active as normal faults in the Taconian foreland, both these faults were later inverted during Acadian orogenesis. The present reverse offset on the Piccadilly Bay Fault was previously interpreted as normal offset on the southeast-dipping Round Head Thrust. Our new interpretation is consistent with mapping on Port au Port Peninsula and north of Stephenville, where all basement-involved faults are inverted and display reverse senses of motion. It also explains spatially restricted, enigmatic reflections adjacent to the faults as carbonate conglomerates of the Cape Cormorant Formation or Daniel’s Harbour Member, units associated with inverted thick-skinned faults. The K-39 well, which targeted the footwall of the Round Head Thrust, actually penetrated the hanging wall of the Piccadilly Bay Fault. This distinction is important because the reservoir model invoked for this play involved preferential karstification and subsequent dolomitization in the footwalls of inverted thick-skinned faults. The apparent magnitude of structural inversion across the Piccadilly Bay Fault suggests other possible structural plays to the northeast of K-39.
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Vannucchi, Paola. "Segmented, curved faults: the example of the Balduini Thrust Zone, Northern Apennines, Italy." Journal of Structural Geology 21, no. 12 (December 1999): 1655–68. http://dx.doi.org/10.1016/s0191-8141(99)00123-6.
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